1. Technical Field
The invention relates to bar screens for screening a flow of wastewater, and more particularly to bar screens having a bar rack.
2. Related Prior Art
The processing of wastewater in industrial or municipal wastewater treatment plants or pumping stations commonly includes the use of a bar screen located in a channel conducting a flow of wastewater. Bar screens remove various sizes of solid waste carried by the wastewater so that such solids do not damage or otherwise compromise the operation of equipment or processes located downstream of the bar screens. One type of bar screen for performing such waste removal includes a bar rack, which is an array of spaced-apart bars that extends across the flow of wastewater.
Bar racks fall into one of three general classifications: trash racks, coarse screen bar racks, and fine screen bar racks. A trash rack has an effective screen opening between bars of approximately 1-1/2" to 4.0" and a coarse screen bar rack has an effective screen opening of approximately 3/8" to 1-1/2". A fine screen bar rack has an effective screen opening of less than approximately 3/8". A fine screen bar rack can be used to remove fibers and other relatively small sized waste objects which are carried by a flow of wastewater and which otherwise might pass through a coarse bar rack.
While it is important that bar screens remove large floating or suspended solids which might present difficulty for the processing of the wastewater, it is at the same time important to allow smaller solids to pass through the screen to be treated in normal wastewater processing. Accordingly, the selection of an appropriate bar rack for a bar screen will depend largely on the operating environment of the bar screen and on the processing equipment located downstream of the bar screen.
Examples of various prior art bar screens which include bar racks are illustrated in Vol. 1 of Envirex Water and Wastewater Treatment Equipment, (Binder 315), published by Envirex, Inc., 1901 South Prairie Avenue, Waukesha, Wis. 53186-7360. An example of a fine screen bar rack is disclosed by U.S. Pat. No. 4,184,957, which issued to Botsch on Jan. 22, 1980.
Bar screens also typically include mechanical apparatus for cleaning the bar rack and for removing waste collected by the bar rack. Such mechanical apparatus can include a cleaning rake that is supported by the bar screen for movement along the bar rack. It is important to the effective operation of a bar screen, and to the overall performance of the wastewater treatment process, that the solids collected by a bar rack be removed. A broken or ineffective cleaning rake can adversely affect the performance of such processes.
The above-identified Envirex publication illustrates bar screens equipped with cleaning rakes for cleaning associated bar racks. Also, U.S. Pat. No. 4,184,957, which issued to Botsch on Jan. 22, 1980, illustrates a bar screen including a bar rack and a cleaning rake for removing screenings from the bar rack.